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Atmospheric Sciences & Global Change
Research Highlights

October 2014

Particle Profusion Conclusion

Global model comparison project finds large diversity of organic aerosol representations

Aerosol particle diversity in models
Model Diversity. The spatial distribution of the ratio of the organic aerosol mass (including the elements beyond carbon) to the carbon aerosol mass from three models differs substantially, indicating very different simulated organic carbon compositions. Enlarge Image.

Results: Variety might be the spice of life, but it also presents a large challenge when modeling the climate. More than 70 researchers from 46 international institutions compared the ability of 31 models to simulate comprehensive physical and chemical characteristics and lifecycle of carbon-containing atmospheric vapor and particles. The researchers, including several from Pacific Northwest National Laboratory, found differences of more than an order of magnitude in the simulated global atmospheric payload of these tiny particles. The research found little evidence that more complex simulations designed to study human impacts on organic aerosol are more accurate than simpler representations.

"This study clearly demonstrates the need for more effective use of organic aerosol data to constrain model simulations," said PNNL atmospheric scientist Dr. Steve Ghan, a co-author of the research.

Why It Matters: They are described as tiny but mighty. Particles in our atmosphere too small to see with the naked eye have a large influence on our climate. Most are carbon-containing, many of which are emitted from burning fossil fuels. They are important to the climate because most of them are efficient at scattering sunlight and providing the seed for cloud droplets. Scientists who model the climate find that representing these particles in a global climate model is extremely challenging because of the large diversity in the particles' chemical makeup and the wide variety of sources that emit organic vapors and particles into the atmosphere.

Nailing down the human influence on organic particles is particularly difficult because human activities produce both direct emissions of organic compounds, and other compounds that influence organic compounds emitted from natural sources, such as trees and vegetation. Solving this climate modeling challenge will provide important information and tools for those who want to understand our climate's future.

Methods: The study is one of many global aerosol model studies performed as part of the international Aerosol Comparisons between Observations and Models (AeroCom) project. The researchers adapted the results from many aerosol models to a common format and stored the data in a repository, where it can be easily accessed. Researchers can use the data to compare with other compilations of measurements of organic aerosol concentration, mostly from Europe and the United States.

While sources of organic vapor have been studied for two decades, direct emissions of organic particles are neglected in most models because the emissions are poorly understood. These primary emissions will be added to more models, the representation of the semi-volatile nature of some classes of organic compounds will be added, and new understanding of the viscous coating of organic aerosol will be applied to the models. Data from poorly sampled tropical, boreal, southern hemisphere and remote marine regions will be added to the database.

What's Next? The data will be available for additional studies working to better constrain the emissions, chemistry, transport and removal of organic aerosol and its vapor precursors in climate models.

Acknowledgments

Sponsors: Development of the Community Earth System Model was partially funded by the U.S. Department of Energy Office of Science, Office of Biological and Environmental Research Scientific Discovery through Advanced Computing (SciDAC) Program and by the Office of Science Earth System Modeling Program.

Research Team: Richard Easter, Steve Ghan, Xiaohong Liu, Rahul Zaveri and Kai Zhang, PNNL. For a full team list, see the journal reference.

Research Area: Climate & Earth Systems Science

Reference: Tsigaridis K et al. 2014. "The AeroCom Evaluation and Intercomparison of Organic Aerosol in Global Models." Atmospheric Chemistry and Physics 14: 10845-10895. DOI:10.5194/acp-14-10845-2014


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